1. Field of the Invention
The present invention relates to a method and an apparatus for heat processing of a substrate.
2. Description of the Related Art
In the process of fabricating a semiconductor device, for example, an interlayer dielectric is formed by a so-called SOD (Spin on Dielectric) system. In this SOD system, coating processing for coating a semiconductor wafer with a coating solution, heat processing for vaporizing a solvent in the coating solution, cure processing for curing a coating film, and the like are performed.
The cure processing of the coating film is performed by heating the wafer, on which the coating film is formed, to a high temperature of approximately 450xc2x0 C. to 500xc2x0 C., for example, and rapidly cooling the wafer nonstop to a normal temperature of approximately 23xc2x0 C., for example, in a processing unit in which a low-oxygen atmosphere is maintained so that the coating film formed on the wafer is not oxidized.
However, if the wafer with a high temperature of approximately 450xc2x0 C. is rapidly cooled to the normal temperature of approximately 23xc2x0 C., cracks, a warp, and the like are sometimes caused in the cured coating film. As a result, there is a fear of a drop in the quality of products and a decline in yield.
The present invention is made in view of the aforesaid point, and its object is to provide a heat processing method for preventing a sharp decrease in the temperature of a substrate such as a wafer in cooling processing after heating in cure processing of a coating film and the like and a heat processing apparatus for carrying out the heat processing method.
To attain the aforesaid object, a heat processing method of the present invention is a method for subjecting a substrate on which a coating film is formed to heat processing, comprising the steps of: heating the substrate to a predetermined high temperature; and decreasing the temperature of the substrate to a predetermined low temperature, wherein in the step of decreasing the temperature of the substrate to the low temperature, a first step of decreasing the temperature of the substrate from the predetermined high temperature to a predetermined intermediate temperature which is a temperature between the predetermined high temperature and the predetermined low temperature and a second step of decreasing the temperature of the substrate from the predetermined intermediate temperature to the predetermined low temperature are performed separately.
According to such a method for heat processing of the substrate, the step of decreasing the temperature of the substrate, which is heated to the high temperature, to the predetermined low temperature is divided into two stages, and hence the temperature of the substrate heated to the high temperature is first decreased from the predetermined high temperature to the predetermined intermediate temperature, and after reaching the intermediate temperature, decreased from the intermediate temperature to the predetermined low temperature. Thus, compared with the aforesaid case where the temperature of the substrate is rapidly decreased nonstop from the high temperature to the low temperature, the temperature decreasing speed of the substrate is reduced, whereby cracks, a warp, and the like caused by the rapid cooling of the substrate can be prevented.
If the first step further comprises the step of reducing the temperature decreasing speed, cracks and the like caused by rapid cooling can be further prevented. It should be mentioned that the temperature decreasing speed indicates the temperature of the substrate decreasing per unit hour. Moreover, it can be proposed that a reduction in temperature decreasing speed is controlled, for example, so that the set temperature of a heater for the substrate is gradually decreased and finally decreased to the aforesaid predetermined intermediate temperature.
A heat processing apparatus of the present invention is a heat processing apparatus for performing heat processing of a substrate, comprising: a first plate for mounting the substrate thereon and heating the substrate to a first predetermined temperature; and a second plate for mounting the substrate thereon and decreasing the temperature of the substrate to a second predetermined temperature lower than the first predetermined temperature, the second plate being provided with a heater for maintaining the second plate at the second predetermined temperature. It should be mentioned that the second predetermined temperature means a temperature not less than a normal temperature, for example, 23xc2x0 C.
According to the apparatus for heat processing of the substrate, the substrate can be heated to the first predetermined temperature by the first plate, and thereafter the temperature of the substrate can be decreased to the second predetermined temperature by the second plate. Accordingly, the step of heating the substrate to the high temperature and the step of decreasing the temperature of the substrate from the high temperature to the intermediate temperature can be performed. As a result, the substrate which is heated can be cooled gradually in two stages, whereby cracks and a warp caused by rapid cooling of the substrate can be prevented.